The present invention relates generally to the field of telecommunications and, more specifically, to a system for expansion of a telecommunications network with minimal disruption of traffic service on the network.
A fundamental consideration in any telecommunications system design is switching capacity. Switching capacity must be analyzed in terms of current demand and projected demand in order to find a solution that is cost effective for both present and future service. For example, assume that a developing country is in the process of building a basic telecommunications system and intends to provide service to most of its current population. Such a population is most likely geographically distributed among small areas of high density (cities) and larger areas of low density (suburban and rural). In addition, the population is probably growing, but at different rates in different areas. Thus, the challenge for a telecommunications system designer is to provide sufficient switching capacity to support satisfactory service to most or all of the population while also anticipating likely increases in future demand and providing for economical expansion.
A second fundamental consideration in telecommunications system design is providing for the addition of new features or services in the future. Telecommunications equipment and service continues to evolve rapidly, due in large part to the advent of digital technology. Even more dramatic advances are likely in the future, particularly as previously separate industries such as the Internet, cable television and local telephone operating companies integrate services. Again, the challenge is to create a system which economically serves a present need, while also providing flexible and inexpensive ways to integrate new features and services as they become available. Ideally, such new features and services can be added to an existing system without disruption of service, but this has not always been possible.
Several of these fundamental considerations are addressed in a system described in commonly-assigned U.S. Pat. No. 5,544,163, Aug. 6, 1996, entitled EXPANDABLE TELECOMMUNICATIONS SYSTEM, which is incorporated herein in its entirety. Briefly, the patent describes an open, high speed, high bandwidth digital communications network for connecting multiple programmable telecommunications switches to form a large capacity, non-blocking switching system. In a preferred embodiment described therein, the network is implemented using one or more inter-nodal networks which provide a medium for transferring information over the network, and a plurality of programmable switches, each of which appears as a node on the network and serves a group of ports. Additional switches (nodes) may be added to the network as desired to increase the system""s switching capacity.
Each node includes circuitry for transmitting and receiving variable-length, packetized information over the network, thus enabling each node to receive information from or transmit information to all other nodes. The network may carry any type of information present in the system including voice, data, video, multimedia, control, configuration and maintenance, and the bandwidth of the network may be divided or shared across various information types.
In addition, devices or resources other than programmable switches may also act as nodes on the network, thereby gaining direct access to all information passing through the network. More specifically, voice processing resources such as voice mail/message systems or other enhanced service platforms may, by becoming nodes, gain direct access to all ports served by the system without the need for a large central switch. The system""s ability to transfer information of any type, in a readily usable form, at high speed across the network enables any service, feature or voice processing resource which is available at a given node to be provided to any port of the same or any other node.
The programmable switching nodes and the other nodes on an expandable telecommunications system are connected by a physical medium. When it is desired to modify an active inter-nodal network in order to enhance the services or increase the capacity provided by the system, by the inclusion of one or more additional nodes, the physical medium must be modified to accommodate an additional node. More specifically, the physical connections between the nodes in the inter-nodal network adjacent to the area to be expanded must be temporarily physically disconnected in order to connect the new node or nodes into the network. When the physical medium is disconnected, that portion of the inter-nodal network cannot, of course, carry telecommunications traffic. Typically, in such a case, the system, in whole or in part, must be taken out of service, thus leading to possibly unacceptable levels of service interruption.
Also, a new node which is added to the system must be properly configured before beginning operation to avoid undesired interference with other nodes.
There remains a need, therefore, for a telecommunications system which can be expanded by the addition of one or more new nodes with minimal, if any, disruption of telecommunications service provided by the system.
There remains a further need for a method of adding a new node to an existing, active system with essentially no interruption of service in the system.
These and other needs are satisfied by the present invention which provides, in brief summary, a method and system for non-disruptive addition of one or more nodes to an active inter-nodal network in a telecommunications system. In a preferred embodiment the invention is implemented in a method and an associated system which includes a plurality of interconnected nodes, which may be nodes used for telecommunications switching, or other nodes used for voice processing resources such as voice mail/messaging and the like. The nodes are interconnected by an inter-nodal network which carries packetized information among all the nodes served by the inter-nodal network.
Each node has an open mode of operation and a special mode of operation referred to as loopback mode. More specifically, each node has an xe2x80x9cAxe2x80x9d I/O port, which has its own transmit and receive coupling, and a xe2x80x9cBxe2x80x9d I/O port, which has its own transmit and receive coupling. In the open mode of operation, packets traverse between the node and the inter-nodal network by coming into the node through the receive coupling of the xe2x80x9cAxe2x80x9d port and exiting the node by the transmit coupling of the xe2x80x9cBxe2x80x9d I/O port. In loopback mode, one of the I/O ports is effectively disconnected from the system while the other xe2x80x9cloops backxe2x80x9d and functions to both transmit and receive packets using its own transmit and receive coupling and an alternate communication path to continue to pass packets onto and receive packets from the inter-nodal network.
A host is connected in communicating relationship with at least one of the nodes in the system. The host controls certain aspects of the system""s operations by sending messages addressed to all nodes or specific messages to individual nodes. The system is also configured so that one of the nodes is a master node. The master node is capable of sending control messages addressed to the other, non-master, nodes in the network. In accordance with the invention, the master does this messaging, in part, by using a unique inter-nodal network control word. The inter-nodal network control word is a set of bits contained within a frame which in turn contains one or more packets originating from a particular node. In accordance with this aspect of the invention, a unique messaging sequence involves an interplay between messages issued by the host, which may be controlled by a user, and messages issued in turn by the master node, using the inter-nodal network control word. The inter-nodal network control word allows nodes to receive and execute instructions in a synchronized manner while avoiding the necessity of forcing the host to attempt to simultaneously communicate with multiple nodes. In still other circumstances, a non-master node will be enabled to write into the inter-nodal network control word to communicate certain types of information to the master node. This is also a time-saving technique which can by utilized to avoid interruption of system operation.
In accordance with the invention, when it is desired to expand an existing, active inter-nodal network, a location is selected along the inter-nodal network to connect one or more new nodes. As used herein, the term xe2x80x9cnew nodexe2x80x9d shall include one or more new nodes which can be programmable switching nodes, voice processing resource nodes, or other nodes, or a combination thereof as desired in a particular application. The two nodes in the active system which are adjacent to the selected location are identified. The two nodes between which the new node is to be added shall be referred to herein as the xe2x80x9cneighborxe2x80x9d nodes, as they will neighbor the new node when it is added to the system.
The new node is prepared by the host for addition to the network by being programmed with instructions about the installation procedure it needs to follow. The inter-nodal network is then checked to ascertain whether any existing nodes are coincidentally operating in loopback mode. If no existing nodes are operating in loopback mode, the expansion of the system by the addition of the new node may continue. If, on the other hand, there is a node operating in loopback mode, then the fault or other condition causing that node to operate in loopback mode will have to be resolved first. This is because performing the installation procedure while any node is concurrently operating in loopback mode could cause other nodes to become isolated, and thus, cause interruption of service.
Once it is determined that all existing nodes are operating in open mode, the host issues a message addressed to the master node, instructing it to notify the two neighbor nodes, using the inter-nodal network control word, to begin a first synchronized routine to change their respective I/O ports to operate in loopback mode after a predetermined time delay. After this predetermined time period elapses, both neighbor nodes change their respective ports to operate in loopback mode essentially simultaneously. Accordingly, packetized information traversing the inter-nodal network continues to travel through the network uninterrupted except for that portion of the inter-nodal network between the two neighbor nodes. That portion is now temporarily isolated and inactive. Thus, the physical disconnection of that portion of the inter-nodal network can now take place without interruption of the remainder of the network. Thereafter, the new node or nodes are physically connected into the network.
In accordance with another aspect of the invention, the new node follows a sequence of instructions, triggered by certain host-issued messages, which causes the node to wait while the inter-nodal network, which continues to carry normal traffic, is configured to include the new node. This sequence of instructions is a short cut around the normal sequence of messages which would be followed by a node when an inter-nodal network is being brought into service and initialized. In accordance with the present invention, the new node follows the short cut instructions so that it enters the network in a running state as if it had always been in the network. This avoids the new node following its pre-programmed instructions for network initialization.
After the new node is connected into the inter-nodal network and the configurations tasks are accomplished, the two neighbor nodes must return to the open mode of operation out of loopback mode. In a manner similar to the sequence followed to place the two neighbor nodes into loopback mode, both nodes must be brought out of loopback mode approximately simultaneously. Otherwise, if one node returns its respective port to normal mode first, this leaves only one node operating in loopback mode, and the network will not function properly.
In order to avoid this, in accordance with the invention, a message is issued by the host, addressed to the master node, instructing it to notify the two neighbor nodes to commence a second synchronized routine, this time to discontinue loopback mode and return to open mode after a predetermined time delay. The predetermined time delay allows both nodes to receive the instruction and begin the timing sequence prior to either one of them returning to the open mode of operation. In this way, both neighbor nodes, between which the new node is now inserted, return to open mode essentially simultaneously.
After the two neighbor nodes return to open mode, the host sends a message to the new node in response to which the new node attempts to verify that it is recognizable by the master node. The new node does this by sending a message to the master node, using the inter-nodal network control word. The new node waits for an acknowledgment from the master node. When the acknowledgment is received, then a final verification is performed to ascertain that the new node or nodes as well as the neighbor nodes have open ports. Thereafter, the new node can be configured to transmit and receive packets to and from the inter-nodal network, or to perform a redundancy function by being configured in a receive only mode, as desired in the application.